refactor: move project under backend

backend/app/package.json

@@ -0,0 +1,16 @@
+{
+  "name": "capay-app",
+  "version": "0.1.0",
+  "private": true,
+  "main": "src/server.js",
+  "scripts": {
+    "dev": "node src/server.js",
+    "start": "node src/server.js"
+  },
+  "dependencies": {
+    "dotenv": "^16.4.5",
+    "express": "^4.19.2",
+    "ethers": "^6.12.1",
+    "nanoid": "^5.0.7"
+  }
+}